Phospholamban Thiols Play a Central Role in Activation of the Cardiac Muscle Sarcoplasmic Reticulum Calcium Pump by Nitroxyl

Nitroxyl (HNO) donated by Angeli's salt activates uptake of Ca2+ by the cardiac SR Ca2+ pump (SERCA2a). To determine whether HNO achieves this by a direct interaction with SERCA2a or its regulatory protein, phospholamban (PLN), we measured its effects on SERCA2a activation (as reflected in dephosphorylation) using insect cell microsomes expressing SERCA2a with or without PLN (wild-type and Cys -> Ala mutant). The results show that activation of SERCA2a dephosphorylation by HNO is PLN-dependent and that PLN thiols are targets for HNO. We conclude that HNO produces a disulfide bond that alters the conformation of PLN, relieving inhibition of the Ca2+ pump.